1. Technical Field
The present invention relates to electronic circuits in general, and, in particular, to differential amplifier circuits. Still more particularly, the present invention relates to a low-voltage differential amplifier circuit having a wide common mode range.
2. Description of Related Art
A conventional differential amplifier circuit typically includes a pair of field effect transistors with the gates as differential inputs and the drains as outputs. The conventional differential amplifier circuit also includes a current source connected to the sources of the field effect transistors to supply a fixed current to the field effect transistors. During operation, the differential voltage inputs supplied to the gates are compared, and the conductivity of one of the field effect transistors is raised whilst the conductivity of the other transistor is lowered.
Conventional differential amplifier circuits are best operated in a common mode range (CMR) centered around Vdd/2. When outside the above-mentioned CMR, the outputs of conventional differential amplifier circuits may not be acceptable. Such limitation in the CMR tend to restrict the type of applications conventional differential amplifier circuits can be employed.
There are several solutions for increasing the CMR of a conventional differential amplifier circuit. However, none of the solutions allow proper operations from 0.1 to (Vdd−0.2) volt over the entire process, voltage and temperature (PVT) operating range. Consequently, it would be desirable to provide an improved differential amplifier circuit having a relatively wide common mode range.